Inductive coupling is one known method for transferring power across coupled conductors without the need for physical connection between the conductors. An application of inductive coupling is to provide power to a movable vehicle running along a track.
FIGS. 1 and 2 show a schematic representation of a known inductively coupled power transfer (ICPT) system. FIG. 2 is a cross-section through the system. A primary coil or conductive path 1 carries alternating current, typically at a very low frequency (VLF) of about 5-50 kHz. The primary coil 1 has first and second conductors extending along two spaced apart sides 1a, 1b. A power pick-up for such a system includes a secondary coil 2 wound about a magnetically permeable core 3 (preferably a ferromagnetic core) which is located between the sides 1a, 1b. The ferromagnetic core concentrates the magnetic flux from the primary coil 1 and an electric potential is produced across the terminals of the secondary coil 2. The secondary coil 2 is typically tuned by a series or parallel capacitor. This electric potential is then rectified and converted to a required voltage. The ferromagnetic core 3 shown in FIG. 1 is E-shaped. Alternatively, an H-shaped core can and has been used.
The ferromagnetic core 3 and coil 2 may be provided on an electric vehicle that can travel on tracks that follow the path of the primary coil 1, or a set of primary coils 1. The output from the secondary coil 2 may be used to power the vehicle. U.S. Pat. No. 5,293,308 (Boys et al.) describes an ICPT system for an electric vehicle and the contents of this patent are hereby incorporated herein by reference.
One problem with inductive power transfer is the relatively large losses that occur in comparison to power transfer methods involving a direct physical connection. These losses increase the cost of operating any apparatus. It would therefore be advantageous if these losses could be reduced.
It is an object of the present invention to provide an ICPT system, or an ICPT system pick-up that has reduced losses in comparison to existing systems, or at least to provide the public with a useful alternative.
Unless the context clearly requires otherwise, throughout the description, the words “comprise”, “comprising”, and the like, are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense, that is to say, in the sense of “including, but not limited to”.